In addition to publishing under licence, (you have to demonstrate ability to access by the copier, or they can claim independent inspiration) - you could take CDs to the bank and deposit them as safekeeping items (this is a different service from safety deposit boxes which wouldn't work for this purpose). Each copy goes in its own sealed envelope which you sign and date and which you ask to be countersigned by a bank employee of reasonable seniority, across the seal in both cases. That way in the event of any intellectual stealing, you could summon the bank to whatever court case, requiring them to produce the CD together with their records in its regard, thereby proving that any subsequent attempt to publish was later than your own date of conception by this means of evidence. The multiple copies are needed because not every court will accept another courts records in the event of needing to repeat the protection or in the event of awkward multi-jurisdictional cases and the bank needs to understand from you (in writing in advance) why you are making the safekeeping deposit so that they know they have the responsiblity of careful recordkeeping in regard to the item.